In next-generation wireless communication networks, operating frequencies are in many cases much higher than in previous systems. For example, some of these networks operate at frequencies in the range of several GHz, or even higher. Unfortunately, signals that are broadcast or transmitted at these higher frequencies suffer substantially greater attenuation—particularly when passing through intervening objects such as walls in a building—compared to signals at lower operating frequencies. As a result, unless transmitter power levels are substantially increased (which is often not permissible), then communication ranges for wireless devices operating at these higher frequencies are substantially reduced.
One solution to mitigate the problems of these higher frequency bands is the use of directional antennas by the wireless devices. As is well known, when the beamwidth of a transmitting or broadcasting antenna pattern is reduced, an antenna gain is achieved which has an effect as if the transmitter power level has been increased. Similarly, when the beamwidth of a receiving antenna pattern is reduced, an antenna gain is achieved which has an effect as if the received power level has been increased. By employing directional antennas with sufficiently narrow beamwidths (i.e., sufficient antenna gains) for transmission and reception, wireless devices are able to operate at higher frequency bands while still maintaining an acceptable communication range.
An additional benefit of a communication network where wireless devices use directional antennas for transmission and/or reception is spatial reuse. That is, wireless devices may point their antenna beams at different directions and transmit simultaneously without interfering with each other. For example, FIG. 1A illustrates a communication network 10 where only wireless device 12A or wireless device 12C can transmit at any given time. Otherwise, transmissions from wireless device 12A and transmissions from wireless device C will collide at devices 12B and 12D. In contrast, FIG. 1B illustrates a communication network 20 with spatial reuse. In communication network 20, device 22A can communicate with device 22D at the same time while device 22C communicates with device 22B. Compared to communication network 10 illustrated in FIG. 1A, communication network 20 illustrated in FIG. 1B—which employs spatial reuse—can double the spectral efficiency.
To enable spatial reuse, wireless devices must be aware not only of the durations of ongoing transmissions in the wireless network, but also the directions of the transmissions. For example, in FIG. 1B wireless device 22A must know at which direction wireless device 22B's antenna is pointed so that wireless device 22A's transmission will not collide with other transmissions received at wireless device 22B. Moreover, wireless device 22A also has to ensure that transmissions from wireless devices 22B and 22C will not interfere with proper reception of other transmissions (e.g., an ACK from device 22D) at its own receiver.
Therefore, a wireless device in a communication network employing spatial reuse should initiate a new communication only when its proposed communication will not cause interference to ongoing communications in the wireless network.
Accordingly, in a communication network which employs spatial reuse and resource reservations, any new reservations which would cause interference to existing communications should be prevented. And in particular, in a distributed communication network without a central controller which employs spatial reuse and resource reservations, the wireless devices should refrain from establishing new reservations that will cause interference to ongoing communications in the wireless network.
Accordingly, it would be desirable to provide a method and protocol for establishing resource reservations in a communication network employing spatial reuse that ensures that any new reservations do not cause interference to existing communications in the wireless network. It would also be desirable to provide a wireless device which executes a method for establishing resource reservations in a communication network employing spatial reuse that ensures that any new reservations do not cause interference to existing communications in the wireless network.
In one aspect of the invention, a method is provided for reserving a time slot for communication between a first wireless device and a second wireless device in a communication network. The method includes searching information elements in a beacon received from a beaconing device in the communication network to find any existing reservations for the time slot, the information elements identifying wireless devices and associated antenna beams employed in existing reservations. When no existing reservations are found for the time slot, the method includes transmitting an information element for reserving the time slot for communication between the first wireless device and the second wireless device. When one or more existing reservations are found for the time slot, the method includes: searching the information elements in the beacon received from the beaconing device to find any other wireless devices and associated antenna beams communicating in any existing reservations for the time slot, checking a local database of wireless devices and antenna beams to determine whether any antenna beam to be used in a proposed communication between the first wireless device and the second wireless device would interfere with the other wireless devices and associated antenna beams communicating in the one or more existing reservations for the time slot, and transmitting the information element for reserving the time slot for communication between the first wireless device and the second wireless device, when any antenna beam to be used in the proposed communication between the first wireless device and the second wireless device would not interfere with any antenna beam used by any other wireless device in any existing reservations for the time slot.
In another aspect of the invention, a method is provided of reserving a time slot for communication between a first wireless device and a second wireless device in a communication network. The method comprises: determining, at the first wireless device, whether any antenna beam to be used in a proposed communication between the first wireless device and the second wireless device within the time slot would interfere with any antenna beam used by any other wireless device in any existing reservations for the time slot; and transmitting an information element for reserving the time slot for communication between the first wireless device and the second wireless device, when any antenna beam to be used in the proposed communication between the first wireless device and the second wireless device would not interfere with any antenna beam used by any other wireless device in any existing reservations for the time slot.
In still another aspect of the invention, a wireless device adapted to operate in a communication network, comprises: a directional antenna system adapted to communicate in a plurality of different directions in the communication network; and a processor adapted to execute a method comprising the steps of: determining whether any antenna beam to be used in a proposed communication with the second wireless device within the time slot would interfere with any antenna beam used by any other wireless device in any existing reservations for the time slot, and causing the wireless device to transmit an information element for reserving the time slot for communication with the second wireless device, when any antenna beam to be used in the proposed communication between the first wireless device and the second wireless device would not interfere with any antenna beam used by any other wireless device in any existing reservations for the time slot.